JP6498792B2 - Battery charge limit prediction method, battery quick charge method and apparatus using the same - Google Patents

Description

  The present invention relates to a battery charging method and apparatus, and more particularly, to a battery quick charging method and apparatus using stepwise charge current reduction to rapidly charge the battery while extending the life of the battery.

  The present application claims priority based on Korean Patent Application No. 10-2015-0116247 filed on August 18, 2015, and the contents disclosed in the specification and drawings of the corresponding application are all incorporated in the present application. Ru.

  Recently, as the demand for portable electronic products such as laptop computers and mobile phones rapidly increases, and as the demand for electric carts, electric cars, electric bicycles and the like also increases, for high-performance batteries that can be repeatedly charged and discharged Research is actively conducted. More recently, carbon energy has been gradually depleted, environmental concerns have been increasing, and demand for hybrid electric vehicles (HEVs) and electric vehicles (EVs) has been gradually increasing worldwide. Along with this, much attention and research are concentrated on vehicle batteries, which are the core components of HEVs and EVs, and there is an urgent need for technological development for rapid charging that can quickly charge the batteries. In particular, in an EV without an additional energy source, fast charging is a very important performance.

  The process of charging the battery involves passing current through the battery to store charge and energy, such process must be carefully controlled. In general, excessive charge rate (C-rate) or charge voltage permanently degrades the performance of the battery resulting in complete failure or catastrophic failure such as leakage or explosion of highly corrosive chemicals It may cause a failure.

  The conventional battery charging method is a constant current (CC) method in which charging is performed at a constant current from the initial stage of charging to completion, a constant voltage (CV) system in which charging is performed at a constant voltage from the initial stage of charging to completion, and a constant current at the initial stage of charging In the final stage of charging, a constant current-constant voltage (CC-CV) system is used.

  In the CC system, at the beginning of charging, the voltage difference is large and a large current flows. In terms of mere completion of charging, the larger the charging current, the better, but continuously charging with a large current reduces the charging efficiency and affects the life of the battery. In addition, in the CC method, a current such as the initial stage of charging continues to flow in the battery even when charging is completed, so the Li-plating phenomenon of forming a metal plating film is characteristic of lithium (Li) ions. There is a safety problem that occurs and loses the overcharge adjustment function. Therefore, it is inconvenient because the charger and the battery have to be separated quickly if charging is completed. On the other hand, in the CV method, if charging of the battery is completed, the terminal voltage changes largely due to temperature change and heat generation of the battery itself, and it is difficult to set a constant voltage value in advance. There is a disadvantage that the charging time is long because the time battery is charged.

  The most widely used method is the CC-CV method. When the battery is discharged in a large amount, it is charged by CC, and when charging is almost completed, it is changed to CV to prevent overcharging. If “C” is the battery capacity of the charge unit (sometimes denoted Q) A · h, then the current in amps is selected as the fraction of C (or as a multiplier). Generally charge up to 1C. In the case of a lithium battery having a capacity of 700 mAh, charging is completed in about one hour and thirty minutes. However, the charging system must be charged under the conditions suitable for the charging capacity of the charger, and must be charged in a place which can be ventilated smoothly and at a normal temperature (about 25 ° C.).

  The CC system is most advantageous for quick charging. However, if the battery is rapidly charged at a high charge current density, Li is not intercalated on the negative electrode and is deposited, which causes a problem of Li-plating phenomenon. Reactions, changes in the kinetic balance of the battery, etc. may result in future battery degradation. Therefore, there is a need for a technique to achieve rapid charging while not causing the Li-plating phenomenon.

  An object of the present invention is to provide a method of predicting battery charge limit so that Li-plating does not occur.

  Another object of the present invention is to provide a battery charging method and apparatus capable of rapidly charging a battery by the above method.

  In order to solve the above problems, the battery charge limit prediction method according to the present invention comprises the steps of: (a) manufacturing a three-electrode cell comprising a unit cell and a reference electrode; (b) charging the three-electrode cell Measuring the negative electrode potential (CCV); and (c) setting the point at which the negative electrode potential starts to become constant without decreasing as the generation point of Li-plating and setting it as the charging limit.

  In particular, in the graph of the negative electrode potential (CCV) according to the SOC, it is desirable to set a point at which the slope of the negative electrode potential changes as the charging limit.

  By changing the charging rate and repeating the steps (b) and (c), the charging limit at the corresponding charging rate can be obtained and integrated to obtain a charging protocol.

  Further, in order to solve the above-mentioned problems, the battery charging method according to the present invention starts from an initial charge rate higher than 1 C and determines a point at which the negative electrode potential of the battery starts to become constant without decreasing is a generation point of Li-plating. It is a method of charging the battery while stepwise reducing the charging rate by a method of setting as the charging limit and charging at the next charging rate when the charging limit is reached.

  In particular, it is desirable to set a point at which the negative electrode potential starts to become constant without decreasing and / or a point at which the gradient of the negative electrode potential changes is set as the charging limit. And, the initial charging rate may be 1.5C to 5C.

  If the charging limit is reached during charging, the charging rate may be reduced and charging may be performed at the next stage until such time as the SOC of the battery reaches 80%.

  In another battery charging method according to the present invention, a data acquisition step of measuring a negative electrode potential due to SOC for each different charging rate through a three-electrode cell experiment comprising a unit cell and a reference electrode; the negative electrode potential decreases from the obtained data Determining a point which begins to become constant without failure as a point of occurrence of Li-plating and setting it as a charging limit, obtaining a protocol for stepwise changing the charging rate; and charging the battery with the protocol.

  Also at this time, it is desirable to set a point at which the negative electrode potential starts to become constant without decreasing and / or a point at which the gradient of the negative electrode potential changes is set as the charging limit.

  The charging rate of the data acquisition may be in the range of 0.25C to 5C. And, the protocol may have an initial charge rate higher than 1C.

  The protocol may have an initial charging rate of 1.5C to 5C.

  The protocol may include gradually decreasing charge rates, and charge voltage information after the end of charge at each charge rate.

  Furthermore, in order to solve the above problems, the battery charging device according to the present invention outputs a charging voltage input from the power supply unit as a charging current to the battery, and a power supply unit outputting the charging voltage input from a commercial power supply. And charging the battery, and changing the charging current when the charging voltage of the battery reaches a preset level, and controlling the charging current output to the battery to change stepwise. The battery charging unit determines a point at which the negative electrode potential of the battery starts to become constant without decreasing the potential as a generation point of Li-plating, and sets it as a charging limit, according to a protocol for changing the charging rate stepwise The battery charging is performed while the charging current is adjusted stepwise.

  According to the present invention, during the progress of CC charging, a point at which the negative electrode potential starts to fall and does not decrease any further (and / or) the point at which the negative electrode potential declines changes is the generation point of Li-plating. A protocol that changes the charging rate in stages by changing the charging rate to the next charging rate when such a Li-plating occurrence point is set as the charging limit, and such charging limit is reached. Suggest. According to such a protocol, if the battery is charged while the charging current is adjusted stepwise, the battery can be rapidly charged while preventing the occurrence of the Li-plating phenomenon on the negative electrode.

  As described above, according to the present invention, the occurrence of Li-plating of the battery negative electrode can be prevented by the reference that sets the charging limit by determining the point at which the negative electrode potential starts to become constant without decreasing and the occurrence point of Li-plating. Therefore, the life of the battery can be extended and the battery can be charged quickly.

  Since the battery is charged without the Li-plating phenomenon, there is no problem such as a side reaction between the deposited Li and the electrolytic solution, or a change in the kinetic balance of the battery, and the cause of the battery degradation can be prevented. In order to charge with a high charge rate within the limit which does not cause Li- plating, rapid charge can be achieved.

  The point at which the negative electrode potential starts to become constant without decreasing can be different for each cell. The present invention is not the proposal of a uniform charging limit ignoring the characteristics of each cell, but the conditions under which Li-plating occurs during charging are clearly understood by experiments through a three-electrode cell to optimize each cell We propose a new charging method.

BRIEF DESCRIPTION OF THE DRAWINGS The following drawings, which are appended to the present specification, illustrate preferred embodiments of the present invention, and serve to provide a further understanding of the inventive concept as well as the detailed description of the invention. It should not be interpreted as being limited to the matters described in the drawings.
FIG. 5 is a flow diagram of a battery charge limit prediction method according to the present invention. It is a figure showing the structure of the pouch type three electrode cell used for the experiment of the present invention. It is the negative electrode potential graph by SOC obtained by the experiment of this invention, and is the figure which also showed the in-situ visualization analysis result. It is a dV / dQ graph obtained from FIG. It is the cycle life comparison graph performed in order to verify the effectiveness of the charge limit prediction method by this invention. FIG. 2 is a flow diagram of a battery charging method according to the present invention. It is the negative electrode potential by charge rate, and the negative electrode potential at the time of protocol charge based on it. When charging the battery by the method according to the present invention, it is a graph showing the charging rate (charging current) per hour. It is a comparison graph of the battery life by the charge method using the stepwise charge current reduction by this invention, and the conventional CC-CV charge system.

  The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, the present invention is not limited to the embodiments described below, and can be realized in various forms. The present embodiment is provided to complete the disclosure of the present invention and to fully describe the scope of the invention to those skilled in the art.

  In the case of CC type rapid charging, cell degeneration due to Li-plating of the negative electrode surface is the most problematic. Li-plating is more likely to occur as the charge current density (charge rate or charge current) is higher or as the temperature is lower, but if the density of the charge current is lowered to prevent it, the target charge rate can not be achieved. According to the present invention, it is possible to provide a technology for shortening the charging time while not causing the Li-plating phenomenon of the battery.

  FIG. 1 is a flow diagram of a battery charge limit prediction method according to the present invention.

  Referring to FIG. 1, first, a three-electrode cell is fabricated (step S1).

  The three-electrode cell is used to confirm the behavior of each of the negative electrode and the positive electrode at the time of research on the secondary battery, and includes a unit cell and a reference electrode. A commonly known structure can be employed for such a three-electrode cell. Among them, FIG. 2 shows the structure of the pouch type three-electrode cell used in the experiment of the present invention.

  The three-electrode cell 10 has a reference electrode 60 inserted between the negative electrode 20 and the positive electrode 30 with the separation film 40 interposed. The reference electrode 60 may have a plate-like structure like the negative electrode 20 or the positive electrode 30, or may be in the form of a wire as shown so that the current flow can be understood more accurately. In FIG. 2, a wire-type reference electrode 60 such as a copper wire 55 coated with an insulating layer 50 is shown as an example. The three-electrode cell 10 is provided with a stable third reference electrode 60 without the influence of polarization in the battery, and the potential difference with the other electrodes 20 and 30 is measured to make each electrode in-situ (in-situ) It is a useful analytical tool because it can interpret the polarization of

The negative electrode 20, the positive electrode 30, and the electrolyte (not shown) constitute a unit cell. For example, the negative electrode 20 includes a graphite-based negative electrode active material such as graphite; 1 to 5 parts by weight of a conductive material based on 100 parts by weight of the negative electrode active material; and 1 to 5 parts by weight of a polymer binder. The positive electrode 30 includes a positive electrode active material such as LiCoO ₂ ; 1 to 5 parts by weight of a conductive material based on 100 parts by weight of the positive electrode active material; and 1 to 5 parts by weight of a polymer binder. The electrolytic solution is an electrolytic solution of a general composition. The unit cell and the reference electrode 60 are housed in the pouch.

  Next, while charging the three-electrode cell manufactured in step S1, the charge characteristic by the negative electrode potential (CCV) is observed (step S2). Such observation results can be summarized, for example, as a negative electrode potential graph by SOC as shown in FIG. FIG. 3 shows the results obtained while charging the three-electrode cell 10 as shown in FIG. 2 at a charging rate of 3C.

  Generally, the negative electrode potential is lowered while the stage is lowered as Li intercalates into the negative electrode active material during charge. At this time, if the charging current density is increased, the stage is not well observed, but the negative electrode potential is continuously lowered due to the intercalation of Li and the increase in resistance. Also from the results of FIG. 3, it can be confirmed that the negative electrode potential gradually decreases from about 0.75 V and falls to 0 V or less with the progress of charging, and falls to about -0.45 V or so.

  By the way, at the time of charge, the reaction in which Li intercalates in the negative electrode active material and the reaction in which Li-plating is generated are reactions that occur in a competitive manner. The present inventors repeat the experiment that if Li-plating is generated during charging, Li can not intercalate in the negative electrode active material, and after that point, the negative electrode potential does not decrease and is maintained constant. I found it. Therefore, in the present invention, it is proposed to determine a point at which the negative electrode potential does not decrease during charging and begins to become constant as the occurrence point of Li-plating.

  From FIG. 3, it is observed that the area where the negative electrode potential shows a constant plateau (plateau) is observed after a certain point, that is, point B. At this time, it was determined that Li ions which could not be intercalated inside the negative electrode active material were plated on the surface of the electrode (between the negative electrode and the separation membrane). Therefore, in the graph of FIG. 3, point B is set as the charging limit.

  In order to confirm the negative electrode potential change at the time of actual charge and the electrode state at the time of charge, in-situ visualization analysis was also performed while charging the three-electrode cell 10 shown in FIG. In-situ visualization analysis locates the three-electrode cell 10 in the surface observation block cell of the electrochemical reaction visualization confocal system, and observes the intercalation process of the charge and discharge profile and the negative electrode during charge and discharge. ECCS B310 equipment was used in this experiment. Such in-situ visualization analysis results are also shown in the negative electrode potential-SOC graph of FIG.

  In general, in the case of a graphite-based negative electrode, as described above, the SOC reaches 100% of the state in which lithium ions are finally inserted between all the layers through several stages as described above. At this time, if the in-situ visualization analysis is performed, the hue of the electrode active material turns to gold. It is possible to interpret the reaction distribution at the time of charge by the hue change from gray to blue, red and gold before charge.

  In FIG. 3, in the in-situ visualization analysis result at the point A ′ where the negative electrode potential is 0 V in the section where the negative electrode potential is decreasing, Li—plating is completely observed between the separation membrane and the negative electrode. I will not. It can be confirmed that Li is inserted into the negative electrode even at the point A where the negative electrode potential is 0 V or less and in the vicinity of the charging limit according to the present invention, and Li-plating is not observed on the negative electrode surface.

  After the point B, a region where the negative electrode potential shows a constant flat area through the point C is observed. According to the in-situ visualization analysis result of the point C 'where the region completely enters the flat region in the region, Li ions which can not intercalate inside the active material are on the surface of the electrode (between the negative electrode and the separation membrane It can be confirmed that metal lithium is deposited and plated from the side).

  In order to find the point at which Li-plating occurs more clearly, draw a dV / dQ graph as shown in FIG. 4 and change the slope of the negative electrode potential, that is, the point (inflection point) at which the rate of decrease of the negative electrode potential changes. -Set as the charging limit at which plating occurs.

  Thus, from the result of step S2, that is, from the negative electrode potential graph by SOC, the point at which the negative electrode potential starts to become constant without decreasing and (and / or) the point at which the negative electrode potential decreases changes (dV / dQ graph) In the present invention, a point (inflection point) at which the slope of the negative electrode voltage changes is set to be a point of occurrence of Li-plating, that is, a charging limit (step S3).

  By changing the charging rate and performing steps S2 and S3 again, it is possible to obtain the charging limit at the corresponding charging rate. By changing the charging rate in this way and repeating steps S2 and S3 and acquiring the charging limit until the charging end point, for example, the SOC reaches 80%, the information is integrated to set the charging protocol for that cell. You can get it. Charging according to this charging protocol is the quick charging method according to the present invention.

  As described above, in the charge limit prediction method according to the present invention, a three-electrode cell is manufactured to observe the charge characteristics at the negative electrode potential, and when charging with each charge current, the charge limit at which Li-plating does not occur is quantified. Do. Furthermore, the point at which the negative electrode potential starts to decrease without falling is determined as the charging limit, and charging is performed at the next charging rate while charging current is gradually reduced by the charging method when the charging limit is reached. -It is possible to provide a multi-step charging technique in which plating does not occur and the charging time is shortened.

According to the method, charge is maintained until the negative electrode potential falls further to 0 V or less as compared with, for example, the reference to “set negative electrode potential to 0 V or higher (Li ⁺ / Li vs. 0 V)”. Referring to FIG. 3, based on (Li ⁺ / Li vs. 0 V), the SOC is about 15% and the negative electrode potential is 0 V, so only a low SOC can be charged at the same charge current density. According to the invention, the charge limit prediction of the present invention having such a criterion is more effective from the viewpoint of rapid charge which can be charged to SOC 30% at the same charge current density and has to be extensively charged in a short time.

  An experiment was conducted to verify the effectiveness of such a charge limit prediction method. A pouch-type three-electrode cell (10 in FIG. 2) is manufactured, and cycles are made from the point where it is determined that Li-plating is to be formed (point B in FIG. 3) and before (point A) and thereafter (point C). The repeated results are shown in FIG.

  The battery life is a measure of how long the battery can be used, and the unit is the number of cycles (cycle), which is also called cycle characteristics. That is, it indicates how many times the battery can be charged and used, and in the sense of electric energy, one cycle is the time when the battery is used once charged and completely discharged, and the number of cycles is the life.

  FIG. 5 is a diagram showing a change in capacity according to the number of cycles. For long life, it is necessary to maintain the capacity of the battery without significantly reducing even after repeated charge and discharge cycles.

  As can be seen from FIG. 5, after 80 cycles of life test up to point C, if the cell is disassembled, a large amount of Li-plating is observed. On the other hand, in the case of the cell which repeated 80 cycles to A and B point, Li- plating was not observed. Further, as can be seen from the life test results, the capacity retention rate drops to 80% even if the cell charged to the point C is repeated only for 20 cycles, and the capacity retention rate becomes 64% or less after 80 cycles. Thus, it can be seen that Li plating (generated when charging to the point C) generated at the time of charge and discharge degrades the cell life characteristics. As proposed in the present invention, when the cycle is repeated with the point B as the charge limit, the capacity retention rate is maintained, the degradation of the cell can be prevented, and the life can be extended.

  It will be as follows if the battery charge method by this invention derived | led-out based on the experimental result regarding such a charge limit prediction is demonstrated.

  FIG. 6 is a flow diagram of a battery charging method according to the present invention.

  Referring to FIG. 6, a data acquisition step of measuring the negative electrode potential of the battery by the SOC for each of different charging rates is performed (step S10).

  This step can be performed through a three-electrode cell experiment including a unit cell and a reference electrode according to the above-described battery charge limit prediction method according to the present invention.

  If “C” is the battery capacity of the charge unit (sometimes denoted Q) A · h, then the current in amps is selected as the fraction of C (or as a multiplier). For example, the 1 C charge rate means a charge / discharge rate that fully discharges or fills the capacity of a fully charged battery in 1 hour, and may also mean the current density at that time. In recent years, as the functions of electronic devices have diversified, the amount of current used by the devices in a given time has also significantly increased. Accordingly, even better performance is required for batteries used as energy sources. In the case of a portable telephone, although the charge rate and discharge rate of C / 2 were conventionally required in the past, from now on, the function may be further strengthened to demand performance corresponding to the charge rate and discharge rate of 1C. At present, batteries for notebook computers, EVs, PHEVs, etc. require a similar charging rate and a higher discharging rate.

  It is desirable from the viewpoint of quick charging that the charging rate is higher than 1C. However, if the charging is continued with a large current, high heat may be generated inside the battery, and each electrode may form an overvoltage state due to the resistance of the battery. Therefore, the charging rate must be determined in consideration of the type and characteristics of the battery.

  The range of charging rates at the data acquisition stage may vary depending on the type and characteristics of such batteries. For example, the battery for EV can set the initial charging rate to 1.5 C, and can acquire data in the charging rate range of 0.25 C to 1.5 C. As another example, the battery for PHEV (plug-in hybrid electric vehicle) can set the initial charge rate to 3C, and can acquire data in the charge rate range of 0.25C to 3C. Such an initial charging rate and charging rate range may be limited not only by the type of battery but also by the maximum current of the motor actually used in the vehicle.

  As described above, in consideration of the battery characteristics, it is possible to set the initial charge rate to 1.5 C for the EV battery and to 3 C for the PHEV battery. Furthermore, in the battery specifications that require high-speed charge and discharge rates, the initial charge rate can be further increased, for example, up to 5C. Therefore, the initial charging rate may be 1.5 C to 5 C, and the charging rate range of the data acquisition phase in the present invention may be 0.25 C to 5 C.

  As described above, much attention and research are concentrated on vehicle batteries, which are the core components of HEVs and EVs, and at the same time, there is an urgent need for the development of rapid charging technology that can rapidly charge the batteries. In the automotive market, the demand for charging time is getting higher and higher initial charging rates are needed to meet it. From the viewpoint of rapid charging, it is advantageous to increase the initial charging rate, but if the charging rate is too high due to the problems as described above, there is a possibility that each electrode may be in an overvoltage state due to battery resistance. Also, if the charging rate is too high, there is a possibility that the limit (in the case of the present invention, the negative electrode potential of 0 V or less) is reached at the same time as charging starts, and the overall charging time can not be shortened too much. Therefore, improving the initial charging rate must be accompanied by improvement of the battery's resistance characteristics. According to the present invention, the initial charging rate can be increased to 5 C for batteries whose resistance characteristics are improved as compared with batteries that have been widely used conventionally.

  FIG. 7 shows the negative electrode potential according to the charging rate. As shown in FIG. 7, a graph was drawn by measuring the negative electrode potential according to the SOC state while changing the charge rate from 3C to 0.5C.

  Thereafter, from the acquired data, a point at which the negative electrode potential of the battery starts to become constant without decreasing is set as an occurrence point of Li-plating, and a protocol for stepwise changing the charging rate is obtained (step S20). If a point at which the negative electrode potential does not decrease and starts to become constant is set as a point at which Li − plating occurs, Li − plating is not induced on the negative electrode.

  For example, in FIG. 7, a protocol as shown as "stepwise charge" is obtained such that the point at which the negative electrode potential starts to become constant without decreasing is set as the occurrence point of Li-plating. When charged at an initial charge rate of 3 C, Li-plating occurs at a point of SOC 30%. Then, the charging rate is changed to the next charging rate of 2.5 C, and if it is charged, Li-plating occurs at a point of 37% of SOC. Then, the charge rate is changed to the next charge rate of 2.0 C, and if it is charged, Li-plating occurs at a point of SOC 61%. Then, the charge rate is changed to the next charge rate of 1.6 C, and if it is charged, Li-plating occurs at a point of SOC 67%. Then, the charging rate is changed to the next charging rate of 1.0 C and charging is performed, and when reaching the point of SOC 80% determined as the charging completion condition, charging is completed.

  Although the protocol is obtained in this way and the graph of the negative electrode potential according to the SOC changes depending on the type of battery, the method for obtaining the protocol can be applied similarly.

  In the present embodiment, although the case of reducing the charge rate from 3 C to 1.0 C has been described, as described above, the range of the initial charge rate and the range of the charge rate at the data acquisition stage can be freely changed. The rate of decrease may not be 0.5 C, 0.6 C, 0.4 C, etc. as in this embodiment, but may be any value.

  FIG. 8 is a graph showing the charging rate (charging current) with time in the case of charging the battery by the method of the present invention, showing the protocol shown in FIG. 7 in terms of the charging rate by time .

  The charging current of the charger for charging the battery gradually decreases with time from an initial charging rate of 3C to a final charging rate of 1.0C. The maintenance time (t1 to t5) of each charging rate can be changed because the point at which the negative electrode potential starts to become constant without decreasing is set as the occurrence point of Li-plating as described above. As described above, in the present invention, the negative electrode potential according to the charging rate is measured, and the charging limit at which Li-plating does not occur is quantified when charging with each current through it.

  Thereafter, the battery is charged according to such a protocol (step S30). The protocol may include progressively decreasing charge rates, and charge voltage information after the end of charge at each charge rate. According to the present invention, charging can be performed by applying a charging current optimized by a protocol.

  The charging protocol can be implemented using the battery charging device according to the invention. The battery charging device is a power supply unit that outputs a charging voltage input from a commercial power supply; the charging voltage output from the power supply unit is output to a battery as a charging current to charge the battery, and the charging voltage of the battery is The battery charging unit may control the charging current to be changed stepwise so as to change the charging current when the predetermined stage is reached. The battery charging unit sets a point at which the negative electrode potential of the battery starts to become constant without decreasing and setting the point as a point of occurrence of Li-plating, and the charging current is adjusted stepwise by a protocol that changes the charging rate stepwise. Allow battery charging to take place.

  Thus, the logic of the protocol of the charging method according to the present invention can be incorporated into the battery charger and used for charging the battery. The battery charging unit employs a processor for achieving quick charging. According to an embodiment of the present invention, the processor can measure the voltage, current, etc. with high accuracy, to store the logic of the charging protocol in memory, achieve accurate control and preserve the device performance. .

  Further, according to the present invention, since the negative electrode potential has a charging process of controlling so that it does not exceed the occurrence point of Li-plating, the negative electrode generates Li-plating as compared with the general CC-CV charge system. And there is the effect of prolonging the life.

  FIG. 9 is a comparison graph of battery life according to the charging method using stepwise charge current reduction according to the present invention and the conventional CC-CV charging method.

  In the present invention and the prior art, the charging time was made the same, and the discharge was made the same condition (1C-CC), and their respective lives were compared. As shown in FIG. 9, in the conventional case (CC-CV), the capacity retention rate decreases after 75 cycles, and after 100 cycles, the capacity retention rate decreases to about 95%, but the present invention (stepwise charging) In the case of, the capacity retention rate reaches 100% even after 400 cycles.

  The lifetime of such a battery is set by various factors, and the structural stability of the electrode, in particular, the stability of the negative electrode is an important factor. An ideal negative electrode should have high reaction reversibility with lithium ions. If an ideal reversible reaction is performed, there is no change in capacity retention rate with cycles. The charging method using stepwise charge current reduction according to the present invention is found to have higher reaction reversibility than before, which is the result of preventing Li-plating in the negative electrode. As described above, according to the charging method using the stepwise decrease of the charging current of the present invention, it can be confirmed that the battery deterioration is prevented and the life becomes longer than before.

  Such a charging method using stepwise charge current reduction according to the present invention Li-plates a point where the negative electrode potential starts to become constant without decreasing while rapidly charging the battery using an initial charging rate larger than 1 C. Therefore, the battery can be rapidly charged without the occurrence of Li-plating because charging is performed by decreasing the charging rate in stages. Damage to the internal structure of the battery can be prevented, and the battery life can be improved.

The charge limit prediction method and the charge method according to the present invention further reduce the negative electrode potential to 0 V or less as compared with, for example, the reference to "set the negative electrode potential to 0 V or more (Li ⁺ / Li vs. 0 V)". Keep charging until it falls. Compared to the standard of (Li ⁺ / Li vs. 0 V), since it can be charged to a higher SOC at the same charge current density, it is very effective in terms of rapid charging that must be massively charged in a short time.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the specific preferred embodiments described above, and does not depart from the subject matter of the present invention as claimed in the claims. It is needless to say that various modifications can be made by those skilled in the art, and such modifications are within the scope of the claims.

Claims (12)

It is a battery charge limit prediction method, and
(A) A unit cell comprising a negative electrode, a positive electrode, and a separation membrane, and a reference electrode, wherein the reference electrode is inserted between the negative electrode and the positive electrode via the separation membrane, and a three-electrode cell Stage of making
(B) measuring a potential difference between the reference electrode and the negative electrode while charging the three-electrode cell, and measuring a negative electrode potential (CCV) by SOC;
(C) At the same time, the point at which the negative electrode potential with respect to the SOC starts to become constant without decreasing and the inflection point of the negative electrode potential with respect to the SOC are determined as occurrence points of Li-plating and set as charging limits A method of predicting battery charge limit comprising:   Changing the charging rate and repeating the steps (b) and (c) to obtain the charging limit at the charging rate, and combining them to obtain a charging protocol. The battery charge limit prediction method as described in 1. Battery charging method,
A three-electrode cell is provided, comprising a unit cell comprising a negative electrode, a positive electrode, a separation membrane, and a reference electrode, and inserting the reference electrode between the negative electrode and the positive electrode via the separation membrane. ,
Measuring a potential difference between the reference electrode and the negative electrode, measuring a negative electrode potential due to SOC for each different charging rate, and acquiring data;
From the acquired data, at the same time, the point where the negative electrode potential with respect to the SOC starts to become constant without decreasing and the inflection point of the negative electrode potential with respect to the SOC are determined as occurrence points of Li-plating and set as charging limit Obtaining a protocol that gradually changes the charging rate,
Charging the battery according to the protocol.   The battery charging method according to claim 3, wherein the charging rate in the data acquisition step is in a range of 0.25C to 5C.   The battery charging method according to claim 3 or 4, wherein the protocol has an initial charge rate higher than 1C.   The battery charging method according to any one of claims 3 to 5, wherein the protocol has an initial charging rate of 1.5C to 5C.   The battery charging method according to any one of claims 3 to 6, wherein the protocol includes a stepwise decreasing charging rate, and charging voltage information after completion of charging at each charging rate. . A battery charger,
A power supply unit that outputs a charging voltage input from the power supply;
The battery is charged by outputting the charging voltage input from the power supply unit as a charging current to the battery, and when the charging voltage of the battery reaches a preset stage, the charging current is changed, A battery charging unit configured to control the charging current to be output to the battery to change stepwise;
The battery includes a unit battery including a negative electrode, a positive electrode, and a separation membrane, and a reference electrode, and the three electrodes in which the reference electrode is inserted between the negative electrode and the positive electrode via the separation membrane. Equipped with a cell,
The battery charging unit measures the potential difference between the reference electrode and the negative electrode, measures the negative electrode potential due to the SOC for each of different charging rates, and acquires data.
From the acquired data, at the same time, the point at which the negative electrode potential with respect to the SOC starts to become constant without decreasing and the inflection point of the negative electrode potential with respect to the SOC are determined as occurrence points of Li-plating and set as charging limit And get a protocol to change the charging rate in stages,
A battery charging device characterized in that the charging current is adjusted stepwise according to the protocol to charge the battery. The battery charging device according to claim 8, wherein a charging rate in the data acquisition step is in a range of 0.25C to 5C . The battery charging device according to claim 8 or 9, wherein the protocol has an initial charge rate higher than 1C . The battery charging device according to any one of claims 8 to 10, wherein the protocol has an initial charging rate of 1.5C to 5C . The battery charging device according to any one of claims 8 to 11, wherein the protocol includes a charge rate which decreases stepwise and charge voltage information after the end of charge at each charge rate. .